Circuit interrupters or circuit breakers generally include a pair of contacts for conducting and interrupting electrical power to a load, and a detection circuit for sensing earth leakage faults and actuating a mechanism that opens the contacts upon the detection of a fault. A common detection circuit uses a current differential transformer having a secondary winding wound around an annular core. The power conductors and the neutral conductor pass through the annular core of the transformer to provide opposing primary windings. The secondary winding of the transformer provides an output signal representative of the imbalance of the current through the conductors. This imbalance is indicative of an earth leakage fault condition. When a fault condition is present, the detection circuit typically energizes a solenoid that actuates the circuit breaker mechanism to open the contacts. As shown in U.S. Pat. No. 4,598,331 to Legatti, the solenoid is connected in series with an SCR between the neutral conductor (or ground) and a DC power source. The detection circuit provides a signal to trigger the SCR to energize the solenoid. The current continues to conduct through the SCR and energize the solenoid until the contacts of the circuit breaker open, which removes the DC power source. A full-wave rectifier may be connected to the load side of the contacts of the circuit breaker to provide DC power to the detection circuit and solenoid.
A disadvantage of using an SCR to energize the solenoid is that the DC power source and detection must by connected to the load side of the contacts. This arrangement presents a problem when a fault condition is present before contacts are closed. The time it takes for the contacts to trip under such a condition is increased by the time needed to energize the circuit upon application of DC power to the detection circuit.
Another disadvantage of using an SCR is the limited amount of control of the current applied to the solenoid. The current applied to the solenoid through the SCR is dependent upon the time to open the contacts. Any change in the actuation time of the contacts or any sticking of the contacts may damage the solenoid and detection circuit. This is especially true for circuit breakers adapted to interrupt high voltages. Furthermore, the tripping of the circuit breaker assembly removes and therefore, does not allow for any indication of the type of fault detected after the circuit breakers have tripped.
Generally multi-pole circuit breakers include a common trip mechanism for interconnecting a set of circuit breakers such that tripping one will trip concurrently the other circuit breakers. U.S. Pat. No. 4,347,488 to Mune et al. shows a multi-pole circuit breaker having such an arrangement. Each circuit breaker includes a tripping member for releasing a resettable mechanism to open a movable contact. Each pair of tripping members are interconnected by a coupler disposed within a recess defined by the abutting side walls of two adjacent circuit breakers. The trip member is generally U-shaped with one leg engageable with the resettable mechanism.
The disadvantage of this common trip mechanism is it includes a number of small pieces which makes it more costly to manufacture and assemble. Furthermore, the coupler engages the trip member about its pivotal axis, and thus requires relatively high forces to pivot the trip member which may delay the actuation of the trip mechanism. The coupler also does not provide a convenient means to actuate the trip mechanism for an earth linkage detection circuit.
Accordingly, it is an object of the present invention to provide a circuit breaker assembly that improves the reaction time for tripping a circuit breaker in response to an earth leakage fault condition.
It is another object to provide a circuit breaker assembly that minimizes power dissipation of an earth leakage module adapted to open the circuit breakers in response to an earth leakage fault condition.
It is a further object to provide a circuit breaker assembly that provides a continuous fault indication representative of the type of fault condition that tripped the circuit breaker assembly.
It is yet another object to provide a circuit breaker assembly that includes means for tripping the circuit breaker assembly in a safe, controlled manner, especially for circuit breakers that interrupt high voltages.